The invention relates to a semiconductor device with a semiconductor body of which a surface is provided with a barrier layer of Ti.sub.x W.sub.1-x, with 0.1&lt;x&lt;0.3. The invention also relates to a method of manufacturing such a semiconductor device.
A barrier layer of Ti.sub.x W.sub.1-x is used in the manufacture of semiconductor devices, for example, between contact zones of silicon or metal silicides provided in the semiconductor body and aluminium conductor tracks provided on the surface with the object of preventing chemical reactions between silicon and aluminium. These reactions could occur during the subsequent manufacture of the semiconductor device during which the semiconductor body is heated to a comparatively high temperature several more times.
A barrier layer of Ti.sub.x W.sub.1-x is found in practice not to form an absolute barrier. Ti and W from the layer form chemical compounds with aluminium. Although the compounds with tungsten are formed less readily than those with titanium, so that in fact a layer without titanium would be preferable, in practice nevertheless 10 to 30 at. % titanium is added to the layer. This is done to ensure that the layer adheres well to the subjacent substrate and to ensure that the layer forms a low-ohmic contact with the subjacent silicon or metal silicide. It is also done, however, to ensure that the layer can be deposited by means of a practical sputtering deposition process.
In a sputtering deposition process, a slice of semiconductor material is positioned in a reaction chamber opposite to a target of the material to be deposited, upon which a plasma is generated in the vicinity of the target. Ions from the plasma hit the target and detach atoms from it, part of which atoms reach the slice and form a layer there. In a later stage of manufacture of the semiconductor device, the slice is subdivided into a number of separate semiconductor bodies. The atoms detached from the target do not only end up on the slice during the sputtering deposition process, but also on the walls of the reactor chamber, so a layer is also deposited on these walls. When the process is repeated, layers being deposited on other slices, the layer on the walls increases in thickness. If pure tungsten is deposited, a layer with bad adhesion is formed on the walls. Once the pure tungsten layer has reached a thickness of approximately 20 .mu.m on the walls, tungsten particles will flake off from this layer and may end up on the surface of the semiconductor body. Such particles are not desired there. The reaction chamber, accordingly, must be cleaned before the layer on the walls has reached this critical thickness. The addition of 10 to 30% titanium to the layer achieves that the layer on the reaction chamber walls has a much better adhesion and does not start flaking off in practice until after it has reached a thickness of approximately 300 .mu.m. This means that the reaction chamber need not be cleaned so often, which is of great practical advantage.
U.S. Pat. No. 5,019,234 discloses a semiconductor device of the kind mentioned in the opening paragraph in which a barrier layer of Ti.sub.x W.sub.1-x is used with barrier properties which are improved in that the layer is exposed to the air for some time before a layer of aluminium is deposited on it. It is achieved in this way that the layer reacts less readily with the aluminium lying over it.
The use of the known barrier layer has the disadvantage that, if the exposure to air of the barrier layer is to provide a practical improvement of the barrier properties, this exposure must last for some days. This means that the manufacturing process of the semiconductor device is in fact delayed by that same number of days. In addition, exposure to air has the disadvantage that deposition of the barrier layer and of the layer of aluminium to be deposited thereon cannot be carried out in a modern multiple-chamber deposition device. In such a device, a semiconductor slice is transported from one deposition chamber to the other at low pressure, a layer being deposited in each chamber. Sometimes an additional etching treatment is carried out in an extra chamber. In such a device, for example, the surface of the slice may then first be cleaned by etching, then a Ti.sub.x W.sub.1-x barrier layer may be deposited, and finally an aluminium layer may be deposited without the vacuum in the device being broken.